House Extension Cost Hammersmith 2026 | Dominant Construction

QUICK ANSWER: A house extension in Hammersmith typically costs £2,500 to £3,800 per square metre in 2026. A side return extension runs roughly £90,000–£165,000, a single-storey rear extension £110,000–£215,000, and a double-storey rear extension £185,000–£390,000, all figures including design, planning, build, and contingency. Most Hammersmith streets — particularly around Brackenbury Village and St Peter's Square — sit within conservation areas, meaning full planning permission applies rather than permitted development.

Type "extension cost Hammersmith" into Google and you'll find no shortage of instant calculators promising your exact number in 60 seconds, before you've told anyone a single thing about your actual house. We'll be straight with you: no calculator knows what your Victorian terrace is hiding behind that chimney breast, and the number it gives you is a guess dressed up as data. Here's what a genuine house extension costs in Hammersmith, and why the real figure only exists after someone's actually stood in your kitchen.

Hammersmith is dominated by tall Victorian and Edwardian three-storey terraces with steep slate roofs — a housing type that brings both opportunity and cost implications most calculators don't account for. The steep roof pitch common across W6 means genuinely strong loft potential, often suiting a full L-shaped dormer rather than a modest single dormer. It also means solid brick construction that's frequently in need of more remedial work than a quick site photo suggests.

Large parts of north Hammersmith — Brackenbury Village and St Peter's Square in particular — sit within conservation areas, where full planning permission is the norm rather than the exception. Applications go to the London Borough of Hammersmith & Fulham, and where a property borders a neighbour (which is most of Hammersmith), a party wall award is standard practice before work starts.

Extension typeTypical 2026 cost (all-in)

Side return extension

£90,000 – £165,000

Single-storey rear extension

£110,000 – £215,000

Wraparound extension

£175,000 – £330,000

Double-storey rear extension

£185,000 – £390,000

£255,000 – £765,000

These figures include design, planning, build, contingency, and VAT — not just the build cost some calculators quote in isolation, which is how a headline number can look 30% lower than what actually lands on your final invoice. Hammersmith's build costs run slightly above the London-wide average, reflecting local labour rates, scaffold logistics on terraced streets, and the finish level expected on a six or seven-figure property.

Renovation scopeTypical 2026 cost (all-in)

Kitchen only

£26,000 – £82,000

Bathroom only

£15,000 – £51,000

Single room refurbishment

£20,000 – £61,000

Whole house renovation

£184,000 – £459,000

Period restoration (listed or heavily original)

£255,000 – £918,000

The spread on period restoration is wide because it genuinely depends on what's behind the plaster — original lath and lime, Victorian brickwork that needs repointing, or services that were last upgraded before anyone reading this was born. This is precisely the number no calculator can give you honestly, because it requires someone opening up the property to find out.

Given the steep roof pitches across most of W6, a loft conversion is frequently the highest-value square-metre spend available on a Hammersmith terrace — often suiting a full L-shaped dormer that combines a rear dormer with a side extension over the existing outrigger, adding a genuine extra floor rather than a squeezed single room.

Why do online extension calculators give lower numbers than a real quote? Most online calculators quote build cost only, excluding design fees, planning fees, VAT, and contingency — all of which are part of the real, final cost of the project. A genuine quote also accounts for site-specific factors an automated tool can't see, such as existing structural condition or access constraints on a particular street.

Do I need planning permission for an extension in Hammersmith? In most cases, yes. Large parts of Hammersmith, including Brackenbury Village and St Peter's Square, sit within conservation areas where permitted development rights are restricted, meaning a full planning application is required rather than the simplified route available elsewhere.

How long does a house extension take in Hammersmith? Typically 4–7 months for construction once planning permission is secured, with the planning process itself adding a further 8–12 weeks beforehand for a standard application.

Dominant Construction has delivered house extensions, renovations, and loft conversions across Hammersmith and West London for over 15 years — FMB-registered, working to JCT contracts, with a fixed price agreed before work starts, based on an actual site visit rather than a form you filled in online.

Call 020 7118 6155 for a proper consultation, visit us at 185 Fulham Palace Road, W6 8QX, or see recent projects at dominantconstruction.co.uk.